1) Field of the Invention
The present invention relates to an in-circuit emulator system used for developing programs of a microprocessor.
2) Description of the Related Art
An in-circuit emulator is a device that supports the debugging of hardware and software when developing a system on which a microcomputer is mounted. The in-circuit emulator is installed in a target system to be debugged, in place of the microcomputer of the target system, and an in-circuit emulator debugger executed on a personal computer reads contents of a register of the microcomputer and efficiently debugs the target system by tracing an instruction of the software. Therefore, the in-circuit emulator is essential to the development of the system with the microcomputer mounted thereon.
The lowest operating frequency and the highest operating frequency of an operation clock of the microcomputer are set in advance, and a clock frequency suited for a system developed by a user is determined within the set range. However, a plurality of oscillators or resonators are not always prepared in the in-circuit emulator. Therefore, the user is required to prepare an oscillator or a resonator for replacement so as to allow the system to operate with clock frequency other than that of the oscillator or resonator provided in the in-circuit emulator.
In order to solve the above problem, conventionally, an in-circuit emulator includes an internal clock generating circuit that uses a synthesizer having a variable oscillation frequency clock in the in-circuit emulator, in place of the oscillator or the resonator. The in-circuit emulator also includes a control circuit that controls the oscillation frequency of the internal clock generating circuit to supply the controlled oscillation frequency to a microcomputer. This type of in-circuit emulator is disclosed in Japanese Patent Application Laid-Open No. 58-40642.
However, the conventional in-circuit emulator has the following disadvantage. Since the control circuit controls the frequency of the internal clock generating circuit, a user cannot set an arbitrary clock in a simple manner.
Further, according to the conventional art, the in-circuit emulator operates in response to a clock supplied to the microcomputer. Therefore, the conventional in-circuit emulator has a disadvantage in that debugging time changes in proportion to the oscillation frequency of the internal clock generating circuit. That is, if the oscillation frequency of the internal clock generating circuit is high, the debugging time becomes short. If the oscillation frequency thereof is low, the debugging time becomes long.